This application is based on Application No. 2001-341135, filed in Japan on Nov. 6, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a controller for a multiplex winding motor, in which the multiplex winding motor, having a plurality of independent windings in a single motor, is driven by a plurality of inverters to control rotation at variable speeds.
2. Description of the Related Art
When an alternating-current motor is driven at variable speeds, generally, an alternating-current motor having a set of multiphase (three phases in general) windings is driven by a single alternating-current power converter (inverter). FIG. 6 shows the configuration of a current controller for an induction motor according to the above method.
In FIG. 6, in a main circuit, a single voltage applying means 15 is connected to an induction motor 3 including a single set of windings, and a current detector 4 for detecting the output current in the voltage applying means 15 is provided on the output side of the voltage applying means 15. The voltage applying means 15 is composed of a PWM pulse generation circuit 5, which outputs a PWM (Pulse Width Modulation) pulse conforming to a direct-current power supply 1 and an alternating voltage command signal v*, and a drive circuit 2 for outputting a voltage of the direct-current power supply 1 in response to a PWM pulse signal produced by the PWM pulse generation circuit 5. The voltage applying means 15 supplies power to the induction motor 3.
Current controlling means 6 is constituted by a two-phase sine wave generation circuit 7, which uses a primary frequency command for an induction motor as input, uses a rotor speed of xcfx891* for a synchronous motor as input, and outputs a two-phase sine wave reference (phase) signal, a voltage command coordinate converter 8 for performing coordinate conversion from d-q axis component voltage commands Vd* and Vq* of a rotating coordinate system to a three-phase alternating voltage command signal v* of a stator coordinate system, a current component detecting coordinate converter 9 for performing coordinate conversion from each winding alternating current i to d-q axis component currents Id and Iq, and a current controller 11 which uses the component current commands Id* and Iq* as commands and uses the d-q axis component currents Id and Iq as input. The d-q axis component currents Id and Iq are the output of the current component detecting coordinate converter 9.
In the above current controller, a current control system is constituted, in which commands of current magnitude and phase are supplied as an exciting component current command Id*, a torque component current command Iq*, and a primary frequency command xcfx891*, an alternating voltage command signal v* required for each winding of the motor is computed and outputted, current i is applied to the induction motor 3 via the voltage applying means 15, and a detected value i from the current detector 4 is used as a feedback value. An inverter 14 is constituted by the current control means 6, the voltage applying means 15, and the current detector 4.
Meanwhile, when a device for driving a large-capacity alternating-current motor does not have an inverter with a capacity suitable for the capacity of the motor, a multiplex winding alternating-current motor having a plurality of sets of multiphase windings may be driven by a plurality of inverters. According to this method, an inverter having the unit capacity of FIG. 6 can be combined according to the capacity without developing a new large-capacity inverter for large motors having different capacities. Thus, development and manufacturing of inverters can be more efficient, thereby reducing the cost. However, in this method, when current flowing in the sets of windings is unbalanced, an inverter with a larger capacity is necessary as compared with balanced current, or torque ripple and so on occurs. Hence, proposals have been made for applying constant current to sets of windings.
For example, FIG. 7 shows a current controller for a multiplex winding motor disclosed in Japanese Patent Laid-Open No. 5-260792. In FIG. 7, a main circuit has two voltage applying means 15A and 15B connected in parallel with a multiplex winding motor 3 having two sets A and B of windings. Drive circuits 2A and 2B, current detectors 4A and 4B, and PWM pulse generation circuits 5A and 5B have the same functions as those of FIG. 6.
A multiple current control means 6 is constituted by a two-phase sine wave generation circuit 7, which uses a primary frequency command for an induction motor as input, uses a rotor speed of xcfx891* for a synchronous motor as input, and outputs a two-phase sine wave reference (phase) signal, voltage command coordinate converters 8A and 8B for performing coordinate conversion from d-q axis component voltage commands Vda*, Vqa*, Vdb*, and Vqb* of a rotating coordinate system to three-phase alternating voltage command signals va* and vb* of a stator coordinate system, current component detecting coordinate converters 9A and 9B for performing coordinate conversion from winding alternating currents ia and ib to d-q axis component currents Ida, Iqa, Idb, and Iqb, an average current detecting circuit 10 for computing an average value of d-q axis component currents of windings, an average current controller 11 which uses component current commands Id* and Iq* as commands and inputs a deviation of average currents Id bar and Iq bar, the average currents Id bar and Iq bar being outputs of the average current detecting circuit 10, a current unbalance compensating circuits 12A and 12B for inputting a deviation of the average currents Id bar and Iq bar and d-q axis component current in windings to correct unbalanced current in windings, and adders 13A and 13B.
When unbalance is not found on output voltage between the drive circuits, the output of the current unbalance compensating circuits 12A and 12B is 0, so that output voltage is equal between the drive circuits. Meanwhile, when unbalance occurs on the output voltage between the drive circuits, unbalance occurs on the current in windings, resulting in a difference among d-q axis component currents Ida, Iqa, Idb, and Iqb. According to a deviation from an average value of the currents, the current unbalance compensating circuits 12A and 12B output a signal for correcting d-q axis component voltage commands of windings such that a difference in d-q axis component currents of windings is 0. Three-phase alternating current command signals va* and vb* obtained by adding the above signals are outputted from the voltage command coordinate converters 8A and 8B. Thus, control is performed such that windings have equal current values.
As described above, in the controller for the conventional multiplex winding motor, a plurality of voltage applying means is controlled by a single of multiple current control means. Thus, as compared with a unit capacity inverter for a single winding that is shown in FIG. 6, a current control system requires a large change in configuration, and it is difficult to share the use of the current control system with a unit capacity inverter which is used independently. Hence, it has not been possible to make full use of a merit of a unit capacity inverter.
As a method for solving the above-mentioned problem, a method has been devised for controlling current in windings separately for each set. However, according to the above-mentioned current controller for the multiplex winding motor disclosed in Japanese Patent Laid-Open No. 5-260792, the above method causes torque ripple due to interference, which results from unbalance of current phases between windings, so that current control cannot be performed with fast response.
Here, the following will specifically discuss why current control with fast response cannot be obtained due to interference resulting from unbalance of current phases between windings.
For example, as shown in FIG. 1, a set of three-phase windings Ua, Va, and Wa (hereinafter, denoted as subscript xe2x80x98axe2x80x99), which are connected at a neutral point Na, and another set of three-phase windings Ub, Vb, and Wb (hereinafter, denoted as subscript xe2x80x98bxe2x80x99), which are connected at a neutral point Nb, are stored in a stator of the motor without electrical connection. The two sets of windings are not electrically connected but the motor is magnetically connected via a magnetic circuit. The above state is similar to connection of a primary side and a secondary side of a transformer.
Therefore, equivalent circuits of Ua phase and Ub phase, which are arranged in parallel, are configured as FIG. 2. In FIG. 2, reference character Vu denotes terminal voltages from the neutral points, reference character R denotes resistances, reference character ve denotes induction voltages, reference numeral 1 denotes leakage inductance, and reference character M denotes mutual inductance. Further, reference character n denotes a turns ratio of a transformer. Additionally, it should be noted that among these values, particularly values of l and M are different from values used for typical motor control but are equal to values between multiplex two phases arranged in parallel. Moreover, generally in a multiplex winding motor, windings in parallel are equal in winding number, so that n=1 is determined. Besides, at this moment, an equivalent circuit of Va phase and Vb phase and an equivalent circuit of Wa phase and Wb phase are identical to FIG. 2. Thus, when three phases have similar characteristics, even when coordinate conversion is performed on two phases of a rotor dq axis from three phases UVW, an equivalent circuit on the two phases of the dq axis is identical to the equivalent circuit of FIG. 2.
As described above, the plurality of sets of windings is magnetically connected in the multiplex winding motor, so that interference voltage mutually occurs. When the equivalent circuit of the multiplex winding motor having three phases UVW is subjected to coordinate conversion on the two phases of the rotor d-q axis, each of the phases has the circuit configuration of FIG. 2 as discussed above. FIG. 3 is a block diagram showing the equivalent circuit on the d axis. In FIG. 3, vda and vdb respectively denote d axis voltages of the sets a and b of windings and Ida and Iab respectively denote d axis currents of the sets a and b of windings. Further, in FIG. 3, voltages denoted as vda and vdb indicate interference voltages from the other sets of windings. Here, reference character s in FIG. 3 denotes a differential operator of Laplace transform. FIG. 3 shows the equivalent circuit on a rotator d axis. As described in the above explanation, the equivalent circuit on a rotor q axis has the same configuration.
Generally, in vector control of alternating motors, current is controlled separately on rotor dq axes. In a multiplex winding motor, the above-mentioned interference voltage interacts and acts on a current control system as disturbance. As shown in FIG. 3, the interference voltage increases proportionately with a differential value of winding current, so that the interference voltage increases as current is responded faster. Thus, it is not possible to improve the response of the current control system as compared with current control of the conventional single-winding motor. Moreover, a ripple component appears on current for the above reason, resulting in torque ripple.
The present invention is devised to solve the above-mentioned problem and has as its object the provision of a controller for a multiplex winding motor whereby when a single multiplex winding motor is driven and controlled by a plurality of inverters, while each winding is composed of a current control system, interference can be compensated between current control systems of windings.
The controller for the multiplex winding motor having two sets of windings according to the present invention comprises first current control means for controlling current in a first winding of the multiplex winding motor according to a current command value, a first current detector for detecting current flowing in the first winding, first voltage applying means for applying a voltage to the first winding according to a voltage command value outputted from the first current control means, second current control means for controlling current in a second winding of the multiplex winding motor, a second current detector for detecting current flowing in the second winding, and second voltage applying means for applying a voltage to the second winding according to a voltage command value outputted from the second current control means. The first current control means comprises a first current controller for computing a voltage command value based on a current command value and a current detection value from the first current detector, and the second current control means comprises a second current controller for computing a voltage command value based on a current command value and a current detection value from the second current detector. Further, the first current control means comprises a first voltage non-interacting arithmetic section for compensating for a voltage command value from the first current controller by using a voltage command value from the second current controller, and the second current control means comprises a second voltage non-interacting arithmetic section for compensating for a voltage command value from the second current controller by using a voltage command value from the first current controller.
With this configuration, it is possible to compensate for voltage interference between the current controllers, thereby achieving current control with fast response.
Further, the controller for the multiplex winding motor having three or more sets of windings of the present invention comprises a plurality of current control means for controlling current in a plurality of windings of the multiplex winding motor according to a current command value, a plurality of current detectors for detecting current flowing in the windings, and a plurality of voltage applying means for applying a voltage to the windings according to a voltage command value outputted from the current control means. Each of the current control means comprises a current controller for computing a voltage command value based on a current command value and a current detection value from each of the current detectors, and each of the current control means comprises a voltage non-interacting arithmetic section for compensating for a voltage command value from each of the current controllers by using a voltage command value from a current controller for another current control means.
With this configuration, it is possible to compensate for voltage interference between the current controllers, thereby achieving current control with fast response.
Moreover, in the controller for the multiplex winding motor of the present invention, computation of a voltage command in the voltage non-interacting arithmetic sections is accomplished based on a transfer function of an interference voltage generated in the multiplex winding motor.
Moreover, in the controller for the multiplex winding motor of the present invention, computation of a voltage command in the voltage non-interacting arithmetic sections is accomplished by summing voltage commands of the current controllers, the commands being multiplied by coefficients.